Atmospheric Pressure

Measuring Atmospheric Pressure 

The Altimeter

Using A Altimeter

Human Risk At Altitude

With A Solid Foundation In Understanding The Basics Related To The Use Of An Altimeter, This Instrument  Can Become A Very Valued Personal Tool.  Many People Over The past 3 Decades Have Acquired Suunto Personal Wristop Computers And Even Older, Swiss Army Pocket Knives With Accurate Altimeters And Other Handheld Altimeters; But Few Individuals Understand The Huge Potentials Of Their Personal Instrumentation.  Note However, The Consumer Markets Are Filled With "Recreational" Toy-Class Altimeters For The Purpose Of Fun Not Serious Applications.  Below I Offer A Starting Point For Your Own Self-Education.  From Here I Highly Recommend Purchasing Authoritative Written Books Related To Your Various Applications; And Continue To Practice Correct Skill Sets.

Atmospheric Pressure

Atmospheric Pressure, Refers To The Weight Of Air Being Exerted Over The Surface Of The Earth.  The amount of pressure depends on the quantity of air above any specific vertical height within the atmosphere.  Atmospheric pressure reduces as the altitude increases.  The Atmosphere Also Called "Air" Can Be Compressed, which means air near the earth's surface will be compressed by its own weight from the volume above.   If standing at an altitude of 3000-meters(9840 ft) above sea level, there is approximately one-third of the earth's atmosphere beneath.  At an altitude of 5500-meters(18040 ft), the air pressure has reduced by half.   At 11,000 meters (36080 ft), the pressure is again reduced by half.

Measuring Atmospheric Pressure

Atmospheric Pressure, Is The Weight If Air, And Can Be Measured Using A Barometer.  Torricelli (Italian physicist of the 17th century) was the first to demonstrate that air, under mild conditions at sea level, has the same weight as a column of mercury with the same cross section, measuring 760 millimeters in length.  It was then adopted to consider the millimeter length of the mercury column as a measure for air pressure; and is abbreviated using one of the following 'mmHg' or 'Torr'.

The meteorology community thought it was illogical to specify pressure as a measurement of length, and came up with the 'millibar' or 'hectopascal' as units for measuring air pressure.  Eventually these reference units were excepted and used by others.  These units are being used in some barometers and altimeters today.  Today the 'millibar', abbreviated with 'mb' or 'mbar' and the 'hectopascal' with 'hPa' are being used more often.

It Is Important to understand the relationship between all these units of measure:

760 'mmHg', or 'Torr' = 1013.25 mb (mbar) = 1013.25 hPa

Air pressure at sea level is used as a reference point and called "1 atmosphere", abbreviated 'atm'.  1 atm = 14.6956 psi = 101325 Pa = 1.01325 bar = 760 torr.

The Altimeter

The altimeter is a practical device used by many mountaineers, and downhill snow sports enthusiasts to measure altitude and vertical speed.  The Altimeter also indicates changes in barometric pressure caused by the weather.  If the user remains in one place for a while, the tendency of the air pressure provides important information on the development of the weather.

For this purpose it is important to note the following:

  -A drop in air pressure indicates a rise in altitude,
  -A rise in air pressure indicates a decrease in altitude.

The exact definition of altitude provided by the altimeter can be of vital importance to mountain climbers out in bad weather with poor visibility.

To Use The Altimeter Properly,

It Is Essential, To Strictly Observe Several Rules!

Using The Altimeter

To use the altimeter properly, it is essential to strictly observe several rules.   The altitude indicated could otherwise be just an approximate value and not good enough to provide accurate bearings under critical visibility conditions. If you have an altimeter, you must be able to rely on it. It is therefore a good idea for every user to check that the instrument is in correct working order every now and then. For this purpose it is necessary to measure the altitude of two points in the terrain, which are situated close to each other and which are specified exactly in the map. If the difference between the altitudes given in the map and the reading of the altimeter is more than ten meters, it is advisable to have the instrument tested by an expert.

Human Risk At Altitude

The amount of oxygen in the air, reduces parallel to the drop in air pressure.  Therefore, at an altitude of 5500 meters (18040 ft), humans only intake half the amount of oxygen than they would at sea level.  In mountainous areas it is necessary to compensate this oxygen shortage by breathing more quickly.  The reduced amount of oxygen in the air at high altitudes leads to a definite reduction in a person’s physical and mental performance, particularly if this person is not well acclimatized.  The altitude at which such a reduction occurs, varies from person to person. Some mountaineers walk excellently in lower regions, suffer a severe setback at altitudes above 3000 meters (9840 ft) and completely give up at heights in excess of 4000 meters (13120 ft).

Casanova's Tip:

Altimeters Are Designed For Specific Applications, Taking Into Account The Intended Purpose.  Read And Understand The intended Purpose Of A Particular Device Offering An Altimeter. Make Sure It Suites The Specific Application You Intend To Use It For.  Avoid Low-Grade General Consumer Products For Any Serious Application.  Many Of These Type Of products Are Made To look Good For The Sale, With Features Added For The Purpose Of  Selling Appeal.  We Have Found Many Of These Low Grade Products Are Not Durable, Reliable Or Accurate  Outdoors And Some Just Do Not Work From The Package!  We Try To Evaluate Products For Their True Value And Avoid The Low Grade Items.  Be Aware, And Understand The Intended Purpose Of The Item And Its Capabilities And Limitations.

Basic Handheld Altimeter Instrumentation Skills

The "Elevation" Is Know

When The Elevation (The Distance Above "Sea Level") Is Know At A Starting Point, Use The Instrument's Calibration Mechanism To Set Its Reading To This Elevation.  Our Handheld Sun Altimeter/Barometer Makes A Great Tool With Easy-Grip Turning Outside Bezel To Set The Needle Over The Elevation Mark.

The "Elevation" Is Unknown

When The Elevation (The Distance Above "Sea Level") Is Not Know At A Starting Point, A Mechanical Instrument Can Be Set To A Zero Reading, And Used To Measure Vertical Ascent Or Descent From The Starting Point.  Some Microcomputer Based Altimeters Offer A Built-In Sea-Level Reference Point Calibration.

Adjust For Reliability

Be Sure To Adjust The Altimeter At Every Point Of Known Elevation, About Every Hour If Possible; To Reduce Error.  This Is Important, Due To Sudden Atmospheric Pressure Changes.

Navigating

A Quality Handheld Altimeter Can Be Used With A Topographical Map To Determined And Plot The Current Position On The Map; Or To Locate A Position On The Map To The Real World Spot On The Terrain.

Intelligent Dual-Duty Weather Predicting

Predict Weather Changes

Our Handheld Sun Altimeter/Barometer Was Built For intelligent Multitasking From One Instrument, Reducing Total gear Count And Carried Weight!  Learn More, With Included Instructions!

Manual Advantage

No Batteries To Forget About And Die When You Most Need It To Work!  There Are A Few Obvious Advantages To Using A Quality Manual Altimeter, Like No Batteries.  However, After Using A Digital Readout For A While, It Soon Becomes Realized That Viewing A Analog Meter Gives Fast Visual Recognition Of Where The Reading Is Within A Know Range.  After Using Both For A While, A Person Can Tall The Subtle Differences.  Thing Of a Digital Clock.  The World Still Is Filled With Analog Face Clocks.

Now Select Your Library Reference Books Wisely, Read For Personal Understanding And Practice Your Skills.  The World Is IS Ready For Adventures Of A Lifestyle...... And Casanova's Is Here To Share The Passion Of Adventure, With Our Customers.  Become A Preferred Casanova Adventurer Today, By Choosing Us Your Your #1 Resource Outfitter Of Choice.

Thank You, From The Casanova's